[Bug c/69540] add a short info on .so priority in -l

[arkadiusz at drabczyk dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69540

--- Comment #1 from Arkadiusz Drabczyk <arkadiusz at drabczyk dot org> ---
Patch sent for review here:
https://gcc.gnu.org/ml/gcc-patches/2016-01/msg02368.html.